This invention relates to apparatus for controlling the exposure corrections in cameras having automatic exposure controls.
In automatic exposure controlled cameras, the apex indicating values B.sub.V, A.sub.V and S.sub.V of brightness of an object to be photographed, diaphragm value of the lens, and the sensitivity of the film, respectively, are utilized in an electronic circuit which determines and controls the shutter speed T (apex value T.sub.V) according to the apex indicating formula: T.sub.V = B.sub.V + S.sub.V - A.sub.V.
When the values B.sub.V, A.sub.V and S.sub.V have been determined, the shutter speed becomes fixed in accordance with those values, irrespective of the photographer's intention, in special cases, to provide a different exposure. For example, when taking a photograph of a person against a very bright background, e.g. snow-crowned mountains, the above formula will result in the shutter speed being too great for proper photography of the person. This is because the background results in a large value of B.sub.V. Thus a deviation or error exists between a proper exposure value intended to be determined by the photographer and an exposure value automatically determined by the camera, so that it becomes necessary to correct the electric information manually. This type of correction is commonly referred to as a correction of exposure. One method of accomplishing exposure correction is to alter the value of S.sub.V set in the camera. For example, if the film speed dial of a camera is set for film of ASA 200 (S.sub.V =6), when the film in the camera has an ASA of 100 (S.sub.V =5), the shutter speed determined by the circuitry will be halved so that the face of the person who backs against snow-covered mountains will not be underexposed on the film. A problem with this technique is that the film sensitivity indicated is not the true film sensitivity, and errors can result from if the photographer does not remember the true sensitivity of the film loaded in the camera. Therefore, so-called X.sub.V devices have been employed for the exclusive use of making exposure corrections.
Another instance of corrections which the camera can not effect automatically are those which may be considered as being dependent upon the technical level of photographers. Thus, for example, a given photographer with experience may prefer to take all or most photographs at an exposure slightly in excess or slightly below that exchange lens group and the kind of film to be used in a which would be automatically set by the camera based on film speed, brightness, and operature opening. Such correction, which is referred to as setting a reference level, can be made by means of the above-mentioned X.sub.V device. However, because the purpose of the correction in this instance is different than the purpose of typical X.sub.V correction confusion can occur caused in the course of correction of the value X.sub.V, first as in the case of correction of the value S.sub.V. In brief, since the photographer employs a certain kind of lens, when it is desired to correct the reference level by one E.sub.V and take a photograph with a correction made by means of the X.sub.V device, and where it is necessary to make a further correction by means of the X.sub.v device for the purpose of effecting a correction under the above-mentioned photographing conditions, the reference level will deviate from the original value and so confusion is liable to occur. For this reason, it is convenient to separately provide a device capable of effecting correction of reference level (including the indication thereof). This will be referred to hereinbelow as the O.sub.V device.